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Bugfix: multiprocessing queue doesn't pickle _size #107

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Bugfix: multiprocessing queue doesn't pickle _size #107

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e7e2329
Bugfix: context not provided to init for multiprocessing queue subclass
Nov 15, 2019
2390656
Bugfix: util.queue._size was not being pickled properly
Nov 15, 2019
ec5faa3
Respond to PR feedback on util/queue.py:
Dec 27, 2019
401b83d
Fix missing sys import
Jan 7, 2020
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16 changes: 16 additions & 0 deletions util/queue.py
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Original file line number Diff line number Diff line change
Expand Up @@ -18,8 +18,10 @@
# along with this program. If not, see <http://www.gnu.org/licenses/>.


import sys
import multiprocessing
import multiprocessing.queues
from collections import namedtuple


class SharedCounter(object):
Expand Down Expand Up @@ -51,6 +53,9 @@ def value(self):
return self.count.value


QueueState = namedtuple('QueueState', ['queue', 'size'])

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Let's make this class non-public: _QueueState.


class Queue(multiprocessing.queues.Queue):
""" A portable implementation of multiprocessing.Queue.

Expand All @@ -66,9 +71,20 @@ class Queue(multiprocessing.queues.Queue):
"""

def __init__(self, *args, **kwargs):
if sys.version_info >= (3, 4) and 'ctx' not in kwargs:
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Please add a comment here explaining why this is necessary (i.e. why we need multiprocessing.get_context() in Python 3.4+).

kwargs['ctx'] = multiprocessing.get_context()
super(Queue, self).__init__(*args, **kwargs)
self._size = SharedCounter(0)

# __getstate__ and __setstate__ are needed for pickling, otherwise _size won't be copied.
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Let's drop this comment and instead add docstrings to the two methods, e.g. "Returns the contents to pickle for the instance" and "Sets the state of the instance upon unpickling".

def __getstate__(self):
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return QueueState(queue=super(Queue, self).__getstate__(),
size=self._size)

def __setstate__(self, state):
self._size = state.size
super(Queue, self).__setstate__(state.queue)

def put(self, *args, **kwargs):
super(Queue, self).put(*args, **kwargs)
self._size.increment(1)
Expand Down